Polyurethane (PU) has been widely used in commodities due to its abrasion resistance, flexibility and mechanical strength.
Conventionally, PU is prepared by a solvent method. In the solvent method, a significant amount of organic solvents is required, and this not only increases the level of hazardous volatile organic compounds (VOCs) in the product but also raises dependency on fossil fuel. Due to these drawbacks, the solvent method is gradually being replaced by a newly-developed method in which waterborne polyurethane is synthesized. Detailed descriptions of synthesis of waterborne polyurethane can be found in, for example, US Patent Publication No. 2009-0192283.
PU products are not degradable when disposed in the natural environment, and thus treatments such as incineration or landfill are necessary. This increases handling cost and could become a serious environmental problem. To reduce the potential damage to the environment, researchers have attempted to incorporate biodegradable polymeric intermediates into PU. Among the biodegradable polymeric intermediates, polylactide diol is one of the most promising materials. A common scheme is to react lactide with short-chain diols or dicarboxylic acids to replace the terminal functional group of the lactide with hydroxy or carboxylic group by ring-opening polymerization. The molecular weight of the polylactide diols or dicarboxylic acids is controlled by the molar ratio of the initiators to the monomers.
However, it is reported that satisfactory mechanical properties, for example elongation higher than 25%, are not obtainable by merely reacting a single polylactide diol and isocyanate; see Wenshou Wang et al., “Shape memory effect of poly(L-lactide)-based polyurethanes with different hard segments,” Polymer International, Vol. 56, pp. 840-846(2007)).
To resolve the above problem as well as to satisfy the needs for a healthy, environmentally friendly and economical material, the present invention discloses an environmentally friendly method in which biodegradable chains and other long-chain polyols are incorporated into polyurethane to provide a polymer with satisfactory mechanical properties, biodegradability and biocompatibility.